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X-CSE-ConnectionGUID: R2vWS9PFTK23zBK6E7lmqw== X-CSE-MsgGUID: xY2XMY7LRHWhS5zhsWollQ== X-IronPort-AV: E=McAfee;i="6800,10657,11578"; a="62385380" X-IronPort-AV: E=Sophos;i="6.19,220,1754982000"; d="scan'208";a="62385380" Received: from orviesa010.jf.intel.com ([10.64.159.150]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2025 13:45:47 -0700 X-CSE-ConnectionGUID: DSHbdxLfR4qtg2r8GD7LEQ== X-CSE-MsgGUID: +HfUa+lxTZeH71bpyRmXHA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.19,220,1754982000"; d="scan'208";a="180306845" Received: from cmdeoliv-mobl4.amr.corp.intel.com (HELO [10.125.111.54]) ([10.125.111.54]) by orviesa010-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Oct 2025 13:45:47 -0700 Message-ID: <281e8018-5506-4a79-8775-e0de7e58b95f@intel.com> Date: Fri, 10 Oct 2025 13:45:45 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: x86/mm: Finishing off the fix for a should_flush_tlb race To: Stephen Dolan , Andy Lutomirski , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Eric Hagberg , Nick Barnes References: Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/9/25 07:01, Stephen Dolan wrote: > That way, either shootdown sees LOADED_MM_SWITCHING and sends an IPI, or > switch_mm_irqs_off sees the updated tlb_gen. The problem in both cases > is about the *before*-ness in switch_mm_irqs_off: > > - in the latest tree, there isn't enough fencing to enforce this > ordering. Stephen, thank you again for the stunningly great bug report! I'll plan to stick the upstream fix into our x86/urgent pile early next week. > - in the stable kernel trees (6.1, 6.6, 6.12), the code is in the > wrong order. This fix also makes sense to me. It's a bummer that the stable fixes are diverging, but I don't have a better idea. So: Acked-by: Dave Hansen It would be best if you could just submit that patch directly to the stable trees: https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst after the equivalent upstream fix lands (even though it is a different logical patch).